Flatpak: fix extention points, Java auto-detect and add Openjdk21

[zocker-160]

This is based on and ported over from fn2006/PollyMC#131 to FjordLauncher with following changes:

• replaced deprecated / EOL com.valvesoftware.Steam.Utility.gamescope extension
• moved ENV variables from starter script into manifest, this way PATH is set correctly also when I use a custom command inside the Flatpak
• fixed Java 8 appearing twice in the version selector auto-detect function thingy
• added OpenJDK 21 for Minecraft >= 1.20.5
• switched x11 socket to fallback-x11, since wayland is the primary socket to use when available
• added extension point for MangoHud, if installed using

flatpak install org.freedesktop.Platform.VulkanLayer.MangoHud//23.08

the MangoHud checkbox will be available in the UI:

[evan-goode]

Hi, thanks for bringing this up, I noticed your PR on PollyMC.

IMO this kind of thing should be merged upstream to Prism Launcher before being merged to Fjord Launcher (or other Prism derivatives). I'd rather keep Fjord Launcher as close to upstream as possible and only accept patches that relate directly to Fjord's goals insofar as they differ from upstream's (i.e. alternative auth).

Prioritizing contributing to upstream means (1) long-term maintainance of Fjord will be easier and (2) upstream and other forks can benefit from the contributions as well.

So would you consider filing this to Prism Launcher instead? If not, I'd be happy to merge this PR on a separate branch of Fjord and try to upstream the work myself, but you certainly understand the changes better than I do, so you could communicate them better.

[zocker-160]

IMO this kind of thing should be merged upstream to Prism Launcher

Ok yeah I agree with your point, it makes sense to stay as close to upstream as possible.

The reason why I did this PR is mainly, because 1) this Flatpak has not been kept in sync with upstream manifest and 2) I cannot contribute upstream since I have no way of testing if the changes actually work (I have never agreed to the requirement of a MS account, despite paying for this damn game twice, but I digress).

So would you consider filing this to Prism Launcher instead?

Actually I think the only thing that needs to be done is to get the Flatpak manifest in sync in order to have a usable one for FjordLauncher again.